Generally speaking, a vehicle seat is provided with a three-point type seat belt for supporting a body of an occupant at three points so as to ensure safety of the occupant on the seat at a motor vehicle accident. At the accident such as a roll-over (or turnover) or a side collision of the vehicle, it is not rare that the seated occupant receives vertical and transverse shock acceleration so that the head moves to out of position and is damaged by the ceiling, the side window, the door lining panel or the pillars.
At this time, the three-point seat belt restraining the occupant effectively works on posterior or anterior accelerations. Since the three-point seat belt holds the occupant at its three points, it is not effective, as expected, at present against the vertical and transverse accelerations.
In the prior art, as disclosed in Patent Document such as JP-A-2003-261000 (as referred to FIG. 2 and FIG. 7), there has been proposed a technique for developing a side airbag, which is disposed on a side of a vehicle seat, for protecting the seated occupant at the motor vehicle accident such as the roll-over or the side collision.
In the side airbag device of the prior art, as disclosed in the Patent Document, the transverse acceleration can be suppressed at the motor vehicle accident to some extent by the side airbag which is disposed in the space between the occupant and the body side portion of the vehicle. However, there is a problem that only one direction restriction by the side airbag cannot cope with the impact accelerations (or the shocks) in all directions.
In case the sensor is activated by the disturbance in the vehicle position to decide an accident and airbag malfunctions, although not an actual accident such as the roll-over or skid, the expanded airbag cannot be easily restored and is hard to remedy.
There is another defect that it is difficult to store parts needing a relatively large space for storing such as the airbag or the inflator to activate the airbag.
This invention has been conceived in view of the background thus far described, and has an object to provide a occupant restraint device and a occupant restraint system, which can reduce the vertical/transverse impact accelerations, as might otherwise be applied to the back of a occupant, reliably at an accident of the vehicle such as a roll-over or a side collision, thereby to lighten the damage of the occupant, and which can enhance the reusability of the device.